physics
posted by Alyssa .
A point charge of +1 µC is located at x =
−2 cm and a second point charge of −8 µC is located at x = 6 cm.
Where should a third charge of +1 µC be
placed so that the electric ﬁeld at x = 0 cm is
zero?

Call the position of the third charge x.
Write the expression for the total E field.
E = k*10^6*10^4[1/2^2 +8/6^2 1/(x)^2]
Set it equal to zero.
Then solve for x.
1/x^2 = 1/4 + 8/36 = 17/36
x =sqrt(36/17)= 1.46 cm